Proteins have been labeled with radioactive metals such as technetium-99m to produce radiolabeled materials which can be used as radiotracers and radioscanners in humans. For example, the Dugan U.S. Pat. No. 3,812,245 issued May 21, 1974 describes radiolabeled streptokinase and urokinase labeled with .sup.99m Tc and their production by contacting streptokinase or urokinase with an aqueous solution containing .sup.99m Tc ions. The .sup.99m Tc ions are bonded to the streptokinase or urokinase, probably through hydroxyl groups.
It has been found, however, that the .sup.99m Tc ions are not all firmly bonded to the streptokinase or urokinase by the procedure of the Dugan patent, and when the .sup.99m Tc-labeled materials are injected into the blood stream, to locate thromboembolisms, for example, some of the .sup.99m Tc ions become disassociated from the streptokinase or urokinase. These disassociated .sup.99m Tc ions are radioactive and are detected in scanning, thus producing anomalous results.
It is an object of this invention to provide a procedure for labeling proteins with .sup.99m Tc which results in firmly bonded .sup.99m Tc atoms. It is a further object to provide a procedure for labeling proteins with .sup.99m Tc by ligand exchange. Another object is to provide new technetium-labeled proteins. These and other objects are apparent from and are achieved in accordance with the following disclosure.